Continuous, size resolved particle measurements were performed in two houses in order to determine size- dependent particle penetration into and deposition in the indoor environment. The experiments consisted of three parts:

measurement of the particle loss rate following artificial elevation of indoor particle concentrations,

rapid reduction in particle concentration through induced ventilation by pressurization of the houses with HEPA-filtered air, and

measurement of the particle concentration rebound after house pressurization stopped.

During the particle concentration decay period, when indoor concentrations are very high, losses due to deposition are large compared to gains due to particle infiltration. During the concentration rebound period, the opposite is true. The large variation in indoor concentration allows the effects of penetration and deposition losses to be separated by the transient, two-parameter model we employed to analyze the data. For the two houses studied, we found that as particles increased in diameter from 0.1 to 10 µm, penetration factors ranged from ~1 to 0.3 and deposition loss rates ranged from 0.1 and 5 h-1. The decline in penetration factor with increasing particle size was less pronounced in the house with the larger normalized leakage area.